Any attempt to extradite David Drumm fraught with difficulty

Towards the end of the trial of three former Anglo Irish Bank directors at Dublin Circuit Criminal Court last year, a defence lawyer described it as "Hamlet without the prince."

He was referring to David Drumm, the bank's former chief executive, a constant presence in the narrative yet unseen and unheard in court.

That trial concluded with two former Anglo directors, William McAteer and Pat Whelan, being found guilty on 10 counts of providing illegal loans to the so-called 'Maple 10' businessmen to buy shares in the bank. Anglo's former chairman, Seán Fitzpatrick, was acquitted of all allegations brought against him.

Handing down non-custodial sentences to McAteer and Whelan, Judge Martin Nolan said Drumm was the "instigator and author" of the scheme.

But so far the Irish authorities have been frustrated in their attempts to draw Drumm into their long-running investigations into Anglo.

The 48-year-old moved to the United States six months after resigning from the bank in December 2008 and has refused to return to Ireland to be questioned about the events leading up to the spectacular collapse of the institution he led.

The DPP has reportedly been weighing whether to bring charges against Drumm since receiving a file from investigators in late 2011. The question now is whether the conclusion of his bankruptcy proceedings in the US will affect the Irish authorities’ plans.

Any attempt to have him extradited from the US would be fraught with difficulty, however.

For a person to be extradited, prosecutors must guarantee that they will face charges once surrendered to Ireland. There must also be corresponding offences in both countries.

Last year’s Anglo trial was the first time that anyone had been prosecuted under section 60 of the Companies Act 1963, which prohibits a company providing financial assistance to buy its own shares. There is no directly corresponding offence in the US. There are certain restrictions on public companies, including under the 2002 Sarbanes-Oxley Act, but no similar ban on share lending by private firms.

One famous example of US share lending, dating back to the 1980s, involved George W Bush, later to become 43rd US president, who received two low-interest loans from an oil company to buy its shares. The deal allowed Bush to raise enough to buy into the Texas Rangers baseball team, an investment that helped him amass his personal fortune and launch his political career in Texas.

A further complication may be a rule in international law known as the doctrine of specialty, which applies in the extradition treaty between Ireland and the US.

This stops a country prosecuting a person for an offence other than the crime for which they have been brought back under extradition. Specialty is not absolute, however, and it is possible to prosecute the individual on another offence as long as the United States consents.

This may mean that the Director of Public Prosecutions could await the completion of all the investigation files into Anglo before she proceeds with an extradition application, if such an application was deemed appropriate.

The DPP does not deem an investigation complete and ready for charges until investigators have made every effort to interview a suspect and to put the allegations to him to see what, if anything, he might say in his defence.

That is not to say that Drumm cannot be charged without being interviewed; if there is sufficient evidence of a crime, they can charge him. Prosecutors can also seek to invoke some mutual assistance procedures from the US allowing them to interview him there.

In the bankruptcy proceedings, lawyers for IBRC (formerly Anglo) said that Drumm arrived in the US with an E-2 Treaty Investor visa in June 2009.

An Irish citizen can obtain an E-2 visa for a maximum of five years, which would bring Drumm’s visa up to June 2014, though he can apply to have his visa renewed.